Intravascular catheters are used to access target vascular regions from remote vascular access sites to perform a procedure. The design, materials, and construction of particular catheters are primarily directed to allow the catheter to reach the target vascular anatomy while not causing vessel trauma, as well as to perform the catheter's intended function upon the catheter reaching the target anatomy. The catheter often has multiple requirements that may conflict with one another. Consequently, a strong design optimally balances the goals of these requirements.
Many catheters are single lumen catheters wherein the lumen acts as a channel for the delivery of radiopaque or therapeutic agents or for other interventional devices into the blood vessel, and/or for aspiration of blood, thrombus, or other occlusive material out of the blood vessel. Such catheters have physical properties that allow them to be advanced through a vessel access site from a proximal end into vascular anatomy which is often very curved, delicate, tortuous, and remote from the blood vessel access site. These catheters are also designed to be used with adjunctive devices such as guide wires and sometimes smaller catheters positioned in the inner lumen, and to be directed to the target anatomy through vascular access sheaths, guide catheters and sometimes sub-selective guide catheters (i.e. catheters that are specifically designed to go to more distal locations than typical guide catheters). In other words, it is often not a single catheter but a system of catheters, guide wires, guide catheters, and sheaths that allows the user to adequately perform an intended procedure.
Interventions in the cerebral vasculature often have special access challenges. Most neurointerventional procedures use a transfemoral access to the carotid or vertebral artery and thence to the target cerebral artery. However, this access route is often tortuous and may contain stenosic plaque material in the aortic arch and carotid and brachiocephalic vessel origins, presenting a risk of embolic complications during the access portion of the procedure. In addition, the cerebral vessels are usually more delicate and prone to perforation than coronary or other peripheral vasculature. In recent years, interventional devices such as wires, guide catheters, stents and balloon catheters, have all been scaled down and been made more flexible to better perform in the neurovascular anatomy. However, many neurointerventional procedures remain either more difficult or impossible because of device access challenges. In some instances, a desired access site is the carotid artery. Procedures in the intracranial and cerebral arteries are much closer to this access site than a femoral artery access site. Importantly, the risk of embolic complications while navigating the aortic arch and proximal carotid and brachiocephalic arteries are avoided. However, because most catheters used in interventional procedures are designed for a femoral access site, current devices are not ideal for the alternate carotid access sites, both in length and mechanical properties. This makes the procedure more cumbersome and in some cases more risky if using devices designed for femoral access in a carotid access procedure.
U.S. Pat. No. 5,496,294 (the '294 patent) describes a single lumen, three-layer catheter design, including (1) an inner Polytetrafluoroethylene (PTFE) liner to provide a low-friction inner surface; (2) a reinforcement layer formed of a metal coil wire or coil ribbon; and (3) an outer jacket layer. Typically, the three layers are laminated together using heat and external pressure such as with heat shrink tubing. The catheter has multiple sections of varying stiffness such that flexibility increases moving towards the distal end of the catheter. This variation in flexibility may be accomplished by varying the durometer of the outer jacket layer along the length of the catheter. Another method to vary flexibility is by varying the reinforcement structure and/or material along the length of the catheter.
One limitation in the '294 patent and in other existing neurovascular catheter technology is that the devices are designed for a femoral access approach to the cerebral arteries. The pathway from the femoral artery to the common carotid artery and thence to the internal carotid artery is both long and comprises several back and forth bends. The dimensions provided in the '294 patent are consistent with this design goal. However, catheters designed to navigate this route have lengths and flexibility transitions that would not be appropriate for a transcarotid access, and would in fact detract from performance of a transcarotid catheter. For example the flexible sections must be at least 40 cm of gradually increasing stiffness from the distal end to a proximal-most stiff section, to be able to navigate both the internal carotid artery curvature and the bends required to go from the aortic arch into the common and then the internal carotid artery.
Another disadvantage to the catheter construction described in the '294 patent is the catheter's limited ability to have continuous, smooth transitions in flexibility moving along its length. There are discreet differences in flexibility on a catheter where one jacket material abuts another, or when one reinforcement structures abuts another reinforcement structure. In addition, the tri-layer catheter construction of the '294 patent has limitations on the wall-thickness due to the need to be able to handle and assemble the three layers of the catheter during manufacture. In addition, the catheter construction makes it difficult to have a relatively large inner lumen diameter while maintaining properties of flexibility and/or kink resistance to very sharp bends in the blood vessel. As a general rule, the larger diameter catheters also tend to be stiffer in order to remain kink resistant.